I have a dvd RW which i back up my system partition without the profiles and then the profiles with my docs in (each fits on 1 dvd)
i have all my games and large programs on the 2nd partition then all my data on the 3rd.
the best way to back up all your movies and mp3s is to give them to your friends - distributed data back up system
i generally keep a ghost image of my system partition on my data disk or on another computer anyway (and vice versa)
these days data storage is so cheap buying a hdd, while not quite as secure / safe, is fairly viable.
you can always reinstall windows and apps froma ghost image (a normal xp installation with all the updates and all the codecs/ media players and other apps will fit onto a bootable ghost dvd) with a bit of room to spare) and then reinstall all your games and larger apps like photoshop etc, as lon as you have your save files.